The current LTE-A standard defines 2D channel modeling and 2D antenna configurations, which means that only horizontal azimuth angles of departure and arrival but no angles in the vertical direction are considered.
Recently 3D channel modeling is attracting more and more attention, since it provides additional performance gain in the vertical direction in addition to the gain in the horizontal direction. In 3D channel modeling, a 3D antenna configuration is required to provide both horizontal coverage and vertical coverage. A typical application of the 3D antenna configuration is for the coverage of an urban environment with high densities of high buildings. Here a 3D antenna configuration refers to an antenna configuration in which a 3D beam can be generated.
In a Frequency Division Duplex (FDD) system, a user equipment selects the best codeword in a predefined codebook representing the downlink Channel State Information (CSI) and feeds a Pre-coding Matrix Index (PMI) corresponding to the codeword back to a base station (eNodeB). The existing standard Rel-10 has offered codebooks for a 2D antenna configuration, but a design of codebooks for a 3D antenna configuration has been absent so far.